The present invention relates generally to the field of tunable light sources. More particularly, the present invention relates to a method and apparatus for providing high power pulsed optical sources useful for industrial applications such as trimming, marking, cutting, and welding. Merely by way of example, the invention has been applied to a light source with real-time tunable characteristics including pulse width, peak power, repetition rate, and pulse shape. However, the present invention has broader applicability and can be applied to other optical sources.
Pulsed laser sources, such as Nd:YAG lasers have been used to perform laser-based material processing for applications such as marking, engraving, micro-machining, and cutting. Depending on the application and the materials to be processed, the various characteristics of the laser pulses, including pulse width, pulse repetition rate, peak power or energy, and pulse shape, are selected as appropriate to the particular application. Many existing high power pulsed lasers, for example, having pulse energy greater than 0.5 mJ per pulse rely on techniques such as Q-switching and mode locking to generate optical pulses. However, such lasers produce optical pulses with characteristics that are predetermined by the cavity geometry, the mirror reflectivities, and the like and cannot generally be varied in the field without compromising the laser performance. Using such lasers, it is generally difficult to achieve a range of variable pulse characteristics.
Generally, these laser sources emit one or more narrow spectral linewidths associated with the longitudinal modes of the laser cavity. These narrow spectral linewidths can give rise to problems due to Stimulated Brillouin Scattering (SBS) in certain embodiments thereof. A discussion of SBS in optical fibers can be read in “Nonlinear Fiber Optics” by G. P. Agrawal, published by Academic Press.
As an alternative to narrow linewidth laser sources, low-coherence sources have been utilized to minimize SBS. However, conventional low-coherence sources are typically characterized by excessively broad linewidths, for which the optical power available in the spectral band of interest for a particular application is low. Therefore, low-coherence sources provide limited output power.
Thus, there is a need in the art for low-coherence pulsed light sources with improved power output and tunable pulse characteristics.